Floridians might want to bone up. Tuesday, voters will be asked to consider an experiment in direct democracy that aims to alter the course of the state's real estate development.

Amendment 4, the proposed change to Florida's state Constitution, sounds relatively straightforward. It would require voter approval of changes to the lengthy and complex comprehensive plans that guide development in cities, towns and counties across the state, giving voters a direct veto over decisions by elected officials.

But just what that entails, including precisely what would come before voters should the measure pass, and how often, is the subject of considerable uncertainty and acrimonious debate.

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Seven years ago, Palm Beach lawyer Lesley Blackner started Florida Hometown Democracy, the movement to get Amendment 4 on the ballot. Work on pro bono environmental cases, including fighting construction of the Suncoast Parkway, convinced her that city councils and county commissions weren't listening to citizens. Meanwhile, the state agency in charge of growth management, she thought, was a "paper tiger" eviscerated by the Legislature.

"Over time, I just realized that somebody needed to put voters in charge of their comprehensive plans," she said last week. "Because I just don't think these commissions are able to do it, are willing to do it."

From the start, millions poured in to fight her idea, first to Floridians for Smarter Growth, then Citizens for Lower Taxes and a Stronger Economy, which has spent more than $10 million since January.

Hometown Democracy has raised less than $3 million as the Florida Realtors Association, the Florida Chamber of Commerce and big builders funded the opposition. Opponents tried to buy away her signature collectors, change the deadline for citizen petitions, and let those who had signed change their mind. In 2006, the law changed to require a constitutional amendment to earn 60 percent of the vote to pass.

Two weeks before the election, a third of likely voters still hadn't made up their minds. The rest were split.

Also split are experts — and the campaigns — over just what Amendment 4 would do.

In practical terms, it means voters would be confronted with comprehensive plan changes on a ballot — perhaps dozens, if critics are correct.

Proponents contend these would be limited to the big and easy to grasp, such as land-use designation changes to allow a new subdivision outside a county's urban development boundary, or a new park, or a high-density, urban in-fill project. Think Quarry Preserve in Hernando, recently held up by the state, Toytown in Pinellas County, Connerton in Pasco or Triple Creek in Eastern Hernando.

However, the state Supreme Court and the Florida Association of Counties have concluded those votes would also encompass comprehensive-plan elements as arcane as infrastructure improvements, including placement of sewer and drainage lines. The state says about 8,000 comprehensive plan amendments are approved by local governments each year in Florida. (That number soared to 15,000 in 2009, as governments tried to rush in changes before Amendment 4 came to a vote.)

To Amendment 4 proponents — Blackner, some environmental groups and a cross-section of ordinary Floridians who signed petitions to get the measure on the statewide ballot — it's a simple matter of giving voters the ability to rein in what they describe as runaway development.

To opponents — an odd-bedfellows alliance of deep-pocketed developers and landowners, business groups, unions, tea partiers, planners and public officials — the amendment amounts to an indiscriminate blast that, by leaving often complex decisions to the unpredictability of the ballot box, could make matters worse by inhibiting smart planning while stifling development in a state heavily dependent on it for jobs.

But the critics' campaign message also tends to the calamitous: Citing a disputed study commissioned from a well-known economist, they predict the measure would be an economic debacle for the state, while costing taxpayers millions to finance costly elections and pay for the probable lawsuits.

A business-funded group, Florida TaxWatch, has estimated Amendment 4 would mean $45 million to $83 million in additional electoral costs yearly across Florida, with litigation costs running into the tens of millions.

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Hometown Democracy's foes have also seized on the experience of St. Pete Beach, riven by years of litigation after voters — angry over proposals for soaring new hotels — passed charter amendments that required voter approval for certain land use changes.

They eventually scaled back the measure, but the town is still contending with what one city attorney called a "small constellation of suits," including some filed by an Amendment 4 proponent unhappy that voters eventually did approve the redevelopment district.

The current City Council has come out against Amendment 4, although the mayor, Mike Finnerty, supports it.

He moved to Florida in 1993 for the sun and the water, the birds and the fish — and the golf courses. He watches dolphins from his balcony and sees the amendment as a check against "overzealous council members."

He fights characterizations of St. Pete Beach as stifled by its decisions, pointing to a new bank project for Dolphin Village.

But some current and former town officials, and Amendment 4 critics, say St. Pete Beach reveals one of the measure's chief flaws, the basis for several of the town's legal claims: By law, complex plan changes that cover dozens of pages must be boiled down to 75 words on ballots. That would leave municipalities vulnerable to suits contending inaccurate or incomplete summaries, they say.

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Amendment 4 aims squarely at Florida's 1985 growth management act, acclaimed at the time as an innovative approach to balancing development with preservation of quality of life and the environment.

The law requires local governments to have a comprehensive plan laying out every aspect of future development, including not just homes and commercial development but also infrastructure improvements like sewers, ports, parking and transportation, as well as protection of natural areas, standards for community design and historic preservation. The resulting land-use maps govern the local zoning rules that control precisely what can be built and where.

Every six months, local elected officials can approve changes to their comp plans. Every seven years, they are required to update the plans. In large cities, that generates dozens, sometimes hundreds, of often technical amendments hard to comprehend by nonprofessionals. Changes can be, and often are, rejected by regional and state planners.

Critics of growth management say developers have grown adept at gaming the system. Meanwhile, they say, a developer-friendly, Republican-dominated Legislature has chipped away at the act's protections and slashed state planners' budgets.

Blackner sees her proposal as one way out of the cycle, even as some critics, such as St. Petersburg City Council member Karl Nurse, argue the same interests will simply influence the new process — while it slows down changes that are helpful.

Ratification of the proposed Amendment 4 to the Florida Constitution requires "yes" votes in at least 60 percent of ballots cast.

This is the wording voters will see on their ballots:

Title: Referenda required for adoption and amendment of local government comprehensive land use plans.

Ballot summary: Establishes that before a local government may adopt a new comprehensive land use plan, or amend a comprehensive land use plan, the proposed plan or amendment shall be subject to vote of the electors of the local government by referendum, following preparation by the local planning agency, consideration by the governing body and notice. Provides definitions.

PolitiFact Florida

Here's a review of some of the Amendment 4 fact-checks from PolitiFact Florida.

• PolitiFact looked at a claim in a web ad by Hometown Democracy that development ends up costing taxpayers, not benefiting them. We found studies that agreed with that point when it comes to large single-family developments. But other studies found benefits to taxpayers for commercial, industrial and neighborhood in-fill development. We rated it Half True.

• We looked at another claim, by the No on 4 group, saying that Amendment 4 will reduce Florida's economic output by $34 billion annually. A number of experts, even some who oppose Amendment 4, agreed that it's much too early to make a blanket statement about the impact. We pegged this one at Barely True.

• We tracked down a chain e-mail that claims many of the companies opposing Amendment 4 benefited from "humongous" federal tax relief. In a bit of a quirk, it turns out the bulk of the e-mail was lifted from a column by Miami Herald columnist and author Carl Hiaasen, though he had nothing to do with the e-mail. As for the facts, we said Half True. At least a dozen companies that gave hundreds of thousands of dollars to Vote No on 4 also got hundreds of millions of dollars in tax relief.

• The No on 4 group often cites the experiences of the town of St. Pete Beach as an example of what can go wrong if Amendment 4 passes. We agreed that four years of political battle there have created a mess, but we said only Half True to the comparison and warned voters to be wary of linking the town to the amendment. We wrote two other Truth-O-Meter items about St. Pete Beach, which you can read at PoltiFact.com/Florida.